A 2.0A resolution structure for crystals of the gamma form of carboxypeptidase a (CPA) is nearing completion. The electron density map will then be analyzed and possibly refined to improve the quality of the structure. This work is a prelude to work directed at the determination of the crystal structures of enzyme-substrate and enzyme-intermediate complexes of CPA-gamma at sub-zero temperatures. Preliminary work indicates we can readily and reversibly equilibrate CPA crystals with a cryoprotective solvent mixture suitalbe for work to at least minus 80 degrees Centigrade. Other work indicated that CPA crystals can be successfully cooled in this system and other systems to low temperature. As a prelude to further work, including possible structural study, we are attempting to find an efficient, high-yield method for the purification of the T-antigen of SV-40 virus in reasonable quantity. The key to such a method appears to be, in our hands, the initial extraction and breaking of the very tight interaction between T-antigen and the nucleic acids. This accomplished, T-antigens chromatographs as a monomer and with high recovery on a number of standard columns.